The etiology of recurrent aphthous ulceration (RAU), a common disease of the oral mucosa, is still obscure. Local, microbial, viral, systemic, nutritional, and genetic factors have been suggested as underlying the pathogenesis of RAUs.1 The viruses considered as causative agents include herpes simplex, varicella zoster, and Epstein-Barr, none of which can, however, be directly isolated from RAU lesions.2 We have noted an increased prevalence of aphthous ulcerations among patients with measles,3 raising the possibility that RAU may be directly related to measles infection. Previously, an association was noted between measles virus infection and Crohn disease, which is characterized by ulceration of the intestinal mucosa.4 Both Crohn disease and RAU are considered to be immunologically mediated. The purpose of the present study was to investigate whether RAU was associated with the measles virus by determining the expression of measles viral antigens in the oral mucosa of individuals with RAU, and whether any change in the expression of CD46, the receptor for measles virus,5 could be detected in the oral mucosa of individuals with RAU compared with controls.